Most of the reactors used in the oil industry, for example those for the catalytic conversion of hydrocarbons and comprising, for example, fixed or moving catalytic beds, are either of the axial or radial type.
The catalysts usually consist of at least one metal, for example, a metal of the groups VIII, VI A, VII A or of another group, the metal being carried on a conventional carrier (alumina, silica, silica-alumina, etc.)
In a substantially vertical axial reactor whose bottom has a spherical or ellipsoidal shape, the charge or reactants to be treated are supplied from the top of the reactor through a distributor and are passed through a layer of a solid material consisting essentially of the catalyst carrier, this solid material being, for example, in the form of balls; this layer provides for a better distribution of the reactants throughout the catalyst mass. After having passed through the catalyst, the reactants are passed through two layers of different grain size, for example, two layers of balls consisting essentially of the catalyst carrier, the one being used to retain the catalyst while the other one of bigger grain size makes easier the recovery of the products through the collector located at the bottom of the reactor, while sustaining the catalyst and alumina located thereover.
The main disadvantage of the axial reactors, where the reactants are circulated vertically, downwardly, parallel to the axis of the reactor (whence the name axial reactor), is that they require a large cross-section for the catalyst layer, while the height thereof is relatively low, in order to have a low pressure drop; those reactors with bottoms of spherical or ellipsoidal shape have a large volume which makes their use of reduced economic interest.
In the radial reactors, the catalyst bed has the shape of a vertical cylindrical ring, internally limited by a grid retaining the catalyst and externally either by the reactor wall and scallops (or shells), or by another grid of the same type as the internal grid. The reactants are supplied from the top of the reactor and are distributed throughout the catalyst mass, either by scallops or through the empty space between the external grid for retaining the catalyst and the wall of the reactor. The circulation within the catalyst mass is from the exterior to the interior, substantially along the reactor radii (whence the name radial reactor). After having passed through the catalyst bed, the reactants are collected in a cylindrical vertical collector, through the internal grid for retaining the catalyst and a sparsely perforated sheet-iron plate provided for ensuring better distribution of the reactants through the catalyst bed, while avoiding preferential passages therethrough.